Peelable composite thermoplastic sealants in packaging films

ABSTRACT

A peelable sealing structure includes a sealing layer and one or more optional additional layers. The peelable sealing structure includes a sealing surface that is formable into a peelable seal upon contact with a sealing substrate at all temperatures in a peelable seal temperature range. Moreover, the peelable sealing structure comprises a thermoplastic polymer and an additive dispersed within at least a portion of the thermoplastic polymer with the peelable sealing structure defining the sealing surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 12/980,312 filedDec. 28, 2010, now U.S. Pat. No. 8,110,286 issued Feb. 7, 2012, which isa continuation of U.S. application Ser. No. 12/031,450 filed Feb. 14,2008, now U.S. Pat. No. 7,871,697 issued Jan. 18, 2011, which is acontinuation-in-part of U.S. application Ser. No. 11/602,650 filed Nov.21, 2006, now U.S. Pat. No. 7,871,696 issued Jan. 18, 2011,thedisclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to package systems that include a peelableseal, and in particular, the present invention relates to compositionsand methods for forming such peelable seals.

2. Background Art

Packaging is an important feature in selling and marketing mostproducts. Food products, in particular, have rather stringent packagingrequirements in order to preserve freshness and enhance shelf life.Certain medical devices also present strict packaging requirements inorder to preserve sterility of such devices. In such applications, thepackage is typically vacuum-packed or gas-flushed and subsequentlyhermetically sealed. Although efficient packaging of products ismandatory, various aesthetic properties of a product package are alsoimportant. For example, the appearance of a product is important inappeeling to consumers. Moreover, in many applications and, inparticular, for food products reusability and ease of opening of apackage are also important considerations. In many applications, theability to easily open a package will depend on the mechanicalproperties of the seal.

One particularly important packaging structure utilizes a peelable seal.In at least one prior art packaging system, a peelable seal is formed bycoating a heat sealable polymeric material onto a metal foil. Sincepackaging incorporating such seals are often impervious to air andcontaminants, peelable seals must also be impervious to these materials.When a package having a peelable seal is opened, a sealing layer may bepeeled away from a substrate. It is desirable for such peeling to beachievable with a low and relatively constant peel force. The elasticproperties of the peelable seal are such that failure of the seal doesnot occur from flexing and normal handling of the package. In some priorart packaging, peelable seals are constructed from multi-layered sheets.Examples of packaging systems having such seals include tray-type foodpackages, bottles or blister packages, and the like. Although some ofthe prior art peelable sealing packages work reasonably well, it hasbeen difficult to construct packaging systems that consistently formhermetic seals that resist leaking while being easily opened by an enduser. Moreover, such prior art peelable packaging systems tend tooperate over relatively narrow ranges, and in particular narrowtemperature ranges. Narrow sealing temperature ranges tend to result inpackaging defects. For example, on the low end of the usable temperaturerange leaking seals may be formed (not hermetically sealed). On the highend of the usable temperature range, non-peelable seal are formed whichtear when opened.

Accordingly, there exists a need for improved peelable packaging systemsthat resist leaking, provide a hermetic seal, and open easily.

SUMMARY OF THE INVENTION

The present invention solves one or more problems of the prior art byproviding in at least one embodiment a peelable sealing structure. Thepeelable sealing structure of this embodiment advantageously includes asealing surface that is formable into a peelable seal upon contact witha sealing substrate at all temperatures in a peelable seal temperaturerange. Moreover, the peelable sealing structure of this embodimentcomprises a thermoplastic polymer, and an additive dispersed within atleast a portion of the thermoplastic polymer.

In another embodiment of the present invention, a peelable sealingstructure is useful for forming a peelable seal at the opening of acontainer. The peelable sealing structure of this embodiment comprises asealing layer and one or more optional additional layers.Advantageously, the sealing layer includes a functionalized organoclaydispersed with a thermoplastic polymer. The incorporation offunctionalized organoclay particles within commonly used heat sealablethermoplastic polymers is found to provide a consistent peel strengthover a broad range of heat sealing conditions. Moreover, the blend ofcommercially available organoclay polymer concentrates with a wide rangeof polyolefin sealant resins advantageously exhibits a peel strengthinversely proportional to the percent load of organoclay. Althoughsealed interfaces utilizing the sealing layer peels in a consistentpattern, the hermetic integrity of the seal is not compromised even whenthe seal specimens include wrinkles, pleats and gusset configurations invarious bag/pouch package styles.

In another embodiment of the present invention, a packaging systemincorporating the peelable sealing structures of the invention isprovided. The packaging system of the invention includes a containersection and a peelable sealing section attached to the containersection. The sealing section includes the sealing layer of the inventionset forth above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic illustration of an Adhesive Type A failure;

FIG. 1B is a schematic illustration of an Adhesive Type B failure;

FIG. 1C is a schematic illustration of a Delamination Type C failure;

FIG. 1D is a schematic illustration of a Break Type D failure;

FIG. 1E is a schematic illustration of a Break Type E failure;

FIG. 1F is a schematic illustration of an Elongation Type F failure;

FIG. 1G is a schematic illustration of a Peel+Elongation Type G failure;

FIG. 2A is a schematic cross-section of a single layer sealingstructure;

FIG. 2B is a schematic cross-section of a two layer sealing section;

FIG. 2C is a schematic cross-section of a three layer sealing layer;

FIG. 3A is a schematic cross-section of a pouch-like packaging systemincorporating an embodiment of the peelable sealing structure of theinvention;

FIG. 3B is a side view of the pouch-like packaging system of FIG. 3A;

FIG. 4A is a schematic cross-section of a refinement in which a sealingsubstrate includes a second sealing layer;

FIG. 4B is a schematic cross-section of a refinement in which sealingsubstrate 160 includes second sealing layer 170 with peelable seal 162being formed between first sealing layer 152 and second sealing layer186;

FIG. 5A Is a schematic cross-section of a cup-like packaging system thatuses the peelable seeling structures of the invention;

FIG. 5B is a schematic cross-section of a blister packaging system thatuses the peelable seeling structures of the invention and incorporatesmultiple cup-like containers;

FIG. 6 is a diagram illustrating a method of forming the packagingsystems of the invention;

FIG. 7A provides plots of the peel force versus temperature for a topseal formed from a sealing layer having 5 wt % and 6 wt % organoclay;

FIG. 7B provides plots of the peel force versus temperature for sealsmade by the three layer co-extrusion of HDPE, EVOH, and a blend of LLDPEand EVA with and without added organoclay;

FIG. 7C provides a plot of the peel force versus seal formationtemperature for a seal made from a foil laminated to a sealing film;

FIG. 8 is a series of plots for determining the melting temperature(“Tm”);

FIG. 9 is a series of plots for determining the crystallizationtemperature (“Tc”); and

FIG. 10A is a set of x-ray diffraction plots showing the dispersion oforganoclay from Nanoblend 2001 within a sealing layer comprisingpolyethylene;

FIG. 10B is a set of x-ray diffraction plots showing the dispersion oforganoclay from Nanoblend 2101 within a sealing layer comprisingpolyethylene;

FIG. 11 provides plots of seal strength versus seal formationtemperature for seals made by an impulse sealer;

FIG. 12A provides plots of seal strength versus seal formationtemperature for seals made from polyethylene or a blend of polyethyleneand EVA made by a conduction sealing method;

FIG. 12B provides plots of seal strength versus seal formationtemperature for seals in which at least one of the sealing layersincludes a blend of polyethylene, EVA, and organoclay;

FIG. 13A provides Table 6 which summarizes the seal strength data forFIGS. 12A and 12B; and

FIG. 13B is a continuation of FIG. 13A;

FIG. 14A is schematic cross-sections illustration of peelable sealshaving one or more folds therein;

FIG. 14B is schematic cross-sections illustration of peelable sealshaving one or more folds therein; and

FIG. 15 is a top view of a packaging system that has folds or bendsincorporated within the seals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Reference will now be made in detail to presently preferredcompositions, embodiments and methods of the present invention, whichconstitute the best modes of practicing the invention presently known tothe inventors. The Figures are not necessarily to scale. However, it isto be understood that the disclosed embodiments are merely exemplary ofthe invention that may be embodied in various and alternative forms.Therefore, specific details disclosed herein are not to be interpretedas limiting, but merely as a representative basis for any aspect of theinvention and/or as a representative basis for teaching one skilled inthe art to variously employ the present invention.

Except in the examples, or where otherwise expressly indicated, allnumerical quantities in this description indicating amounts of materialor conditions of reaction and/or use are to be understood as modified bythe word “about” in describing the broadest scope of the invention.Practice within the numerical limits stated is generally preferred.Also, unless expressly stated to the contrary, percent, “parts of,” andratio values are by weight; the term “polymer” includes “oligomer,”“copolymer,” “terpolymer,” and the like; the description of a group orclass of materials as suitable or preferred for a given purpose inconnection with the invention implies that mixtures of any two or moreof the members of the group or class are equally suitable or preferred;description of constituents in chemical terms refers to the constituentsat the time of addition to any combination specified in the description,and does not necessarily preclude chemical interactions among theconstituents of a mixture once mixed; the first definition of an acronymor other abbreviation applies to all subsequent uses herein of the sameabbreviation and applies mutatis mutandis to normal grammaticalvariations of the initially defined abbreviation; and, unless expresslystated to the contrary, measurement of a property is determined by thesame technique as previously or later referenced for the same property.

It is also to be understood that this invention is not limited to thespecific embodiments and methods described below, as specific componentsand/or conditions may, of course, vary. Furthermore, the terminologyused herein is used only for the purpose of describing particularembodiments of the present invention and is not intended to be limitingin any way.

It must also be noted that, as used in the specification and theappended claims, the singular form “a”, “an”, and “the” comprise pluralreferents unless the context clearly indicates otherwise. For example,reference to a component in the singular is intended to comprise aplurality of components.

Throughout this application, where publications are referenced, thedisclosures of these publications in their entireties are herebyincorporated by reference into this application in their entirety tomore fully describe the state of the art to which this inventionpertains.

The term “organoclay” as used herein means organically modified clay.Typically, such modification renders a clay more compatible andtherefore mixable with polymers.

The term “roughness average” (“R_(a)”) as used herein means the meanheight of a surface as calculated over the entire measured length orarea in accordance with ANSI B46.1. It is usually provided inmicrometers or micro-inches.

The term “peelable seal” as used herein means a seal that has a peelforce of between 0.5 lbs per one inch of sample width and a force thattears the seal. Typically, the upper limit is less than or equal to 5lbs per inch of sample width. In other variation, the upper limit isless than or equal to 4 lbs per inch of sample width or less than thetear strength on the film substrate.

The term “peel force” as used herein means force to separate two layersas defined in ASTM F-88 which is incorporated by references. Forexample, this is the force necessary to separate two layers of one inchwidth by pulling.

The term “seal initiation temperature” as used herein refers to thelowest temperature at which a seal is formed with a peel force of 0.5lbs. per inch. Specifically, the seal initiation temperature is thetemperature of a surface (typically metal) contacting a layer or layersthat are to be sealed thereby promoting such sealing. In somevariations, the surface contacts the layer(s) with a dwell time fromabout 0.5 to 1 seconds with a pressure from 5 psi to 1200 psi.

The term “peelable seal temperature range” means the range oftemperatures at which a seal between two materials is formed such thatthe peel force is between 0.5 lbs per one inch of sample width and aforce that tears the seal as set forth above.

With reference to FIGS. 1A-1G, schematic illustrations are providedillustrating various seal failure mechanisms. In each variation of thesefigures, seal 100 is formed from contact of a section of first sealinglayer 102 with a section of second sealing layer 104 to form a seal.FIG. 1A illustrates the behavior of a peelable seal in accordance withone or more embodiments of the present invention. When a seal betweenlayers 102 and 104 is subjected to a force that acts to pull theselayers apart, layers 102, 104 separate relatively cleanly at separationsurfaces 106, 108. This seal failure is referred to as an Adhesive TypeA failure. FIG. 1B illustrates a seal in which the structure integrityof layer 102 fails when the seal is stressed forming tear 109. This sealfailure is referred to as an Adhesive Type B failure. FIG. 1Cillustrates a seal which includes additional layers to form a multilayerlaminate structure. Layer 110 is attached to layer 102 while layer 104is attached to layer 112. The mode of failure illustrated in FIG. 1C isdelamination at position 114. This seal failure is referred to as aDelamination Type C failure. FIG. 1D illustrates a material failure inwhich layer 104 breaks at position 120 close to a region in which layers102, 104 are still adhered to one another. This seal failure is referredto as a Break Type D failure. FIG. 1E illustrates a material failure inwhich layer 104 breaks at position 122 remote from a region in whichlayers 102, 104 are still adhered to one another. This seal failure isreferred to as a Break Type E failure. FIG. 1F illustrates a materialfailure in which layers 102 and 104 stretch at sections 130, 132 that isnot incorporated in seal 100. This seal failure is referred to as anElongation Type F failure. Finally, FIG. 1G illustrates a materialfailure in which layers 102, 104 separate at seal 100 by a peelingmechanism with a concurrent stretching at sections 136, 138. This sealfailure is referred to as a Peel+Elongation Type G failure. Embodimentsof the present invention advantageously form peelable seals that failvia the Adhesive Type A failure mechanism.

In an embodiment of the present invention, a peelable sealing structureis provided. The peelable sealing structure of this embodiment comprisesa thermoplastic polymer and an additive dispersed within at least aportion of the thermoplastic polymer. The peelable sealing structuredefines a sealing surface that is formable into a peelable seal at alltemperatures within a peelable seal temperature range. In a variation ofthis embodiment, the peelable seal temperature range is from a sealinitiation temperature to a temperature that is that is at least 50° F.degrees above the seal initiation temperature. In another embodiment ofthe present invention, the peelable seal temperature range is from aseal initiation temperature to a temperature that is that is at least75° F. degrees above the seal initiation temperature. In still anotherembodiment of the present invention, the peelable seal temperature rangeis from a seal initiation temperature to a temperature that is at least100 F degrees above the seal initiation temperature. Typically, forpackaging applications the seal initiation temperature ranges from about170° F. to about 350° F. In another variation, for packagingapplications the seal initiation temperature ranges from about 170° F.to about 250° F.

With reference to FIGS. 2A, 2B, and 2C, illustrations of a peelablesealing structure used in the packaging systems of the present inventionis provided. In this embodiment, the peelable sealing structure isattached to a substrate to form a peelable seal or sealing section. FIG.2A is a schematic cross-section of a single layer sealing structure. Inthis variation, peelable sealing structure 150 includes sealing layer152. FIG. 2B is a schematic cross-section of a two layer sealingstructure. Peelable sealing structure 150 includes sealing layer 152 andadditional layer 154. FIG. 2C is a schematic cross-section of a threelayer sealing layer. In this variation, peelable sealing structure 150includes sealing layer 152 and additional layers 154, 156.

It should be appreciated that in each of the variations of FIGS. 2A, 2Band 2C, sealing layer 152 comprises a thermoplastic polymer, and anadditive dispersed within the thermoplastic polymer. In a variation ofthe present embodiments, useful additives have a surface area greaterthan 100 m²/gram and an aspect ratio greater than 10. Additionally,useful additions are crystalline or polycrystalline. Examples of usefuladditives include, but are not limited to, organoclays. Sealing layer152 is adapted to contact a substrate section of a container to form apeelable seal. Such containers may be of virtually any shape that isuseful to package an object. Examples of such shapes include, but arenot limited to, blisters, trays, bags, pouches, and combinationsthereof.

It has surprisingly been discovered that sealing layers formed from thiscomposition have improved and uniform peel performance as described morecompletely below. Sealed interfaces utilizing peelable sealing structure150 peel in a consistent pattern, the hermetic integrity of the seal isnot compromised even when the film specimens include wrinkles, pleatsand gusset configurations in various bag/pouch package styles. Peelablesealing structure 150 exhibits a consistent peelable behavior in thefollowing combinations: 1) sealing layer 152 contacting another sealinglayer of analogous or the same composition; 2) sealing layer 152contacting a structure formed from neat sealant (e.g.organoclay/polyethylene layer against a neat polypropylene layer,organoclay/polyethylene layer against neat polyester layer,organoclay/polyethylene layer against a neat polyethylene layer).Processing aids such as antiblocking agents, antioxidants, slipadditives, and the like are optionally included into the sealing layersand do not affect the peel pattern of sealing structure 150.

Additional layers 154, 156 are used to provide a number of usefulfeatures to the present embodiment. For example, additional layers 154,156 may provide structural support, heat resistance, barrier properties,and improved appearance to packaging systems that incorporate peelablesealing sections. It should also be appreciated that the presentembodiment encompasses, in addition to single layer peelable sealingstructures, multilayer structures having any number of additionallayers. In each variation of the present embodiment, the multilayersealing structures include peelable sealing having the compositionsdescribed herein.

Sealing layer 152 is further characterized by various physical andstructure variations and refinements which depend to some extent on thespecific packaging desired. In one variation of the present embodiment,sealing layer 152 has a thickness from about 6 microns to about 120microns. In another variation of the present embodiment, sealing layer152 has a thickness from about 6 microns to about 30 microns. In stillanother variation of the present embodiment, sealing layer 152 has athickness from about 40 microns to about 120 microns. Sealing layer 152is further distinguished from analogous layers formed without or withinsufficient amounts of organoclay in having a higher degree of surfaceroughness. In one refinement, sealing layer 152 has a surface roughnesscharacterized by a roughness average from about 1500 to about 5000angstroms. In another refinement, sealing layer 152 has a surfaceroughness characterized by a roughness average from about 2000 to about4000 angstroms. It should be readily appreciated that in variations ofthe present invention, the degree and the quality of the surfaceroughness depends both on the methods and process parameters used toform sealing layer 152. The sealing layers of various embodiments alsoexhibit somewhat higher tensile moduli than analogous layers withoutorganoclay. In one refinement, the sealing layer 152 has a tensilemodulus from about 500 to about 2000 MPa.

With reference to FIGS. 3A and 3B, a packaging system incorporating thepeelable sealing structures set forth above is described. FIG. 3A is across-section of a pouch-like packaging system incorporating anembodiment of the peelable sealing structure of the invention. FIG. 3Bis a side view of a pouch-like packaging system incorporating anembodiment of the peelable sealing structure of the invention. Packagingsystem 160 includes container section 162 and peelable sealing section164. Peelable sealing section 164 is attached to container section 162.FIG. 3A depicts an example in which peelable sealing section 164 andcontainer section 162 are continuous, each being formed from the samemultilayer structure (i.e., sheet). Container section 162 can havevirtually any shape that is useful for packaging an object in a pouch.Sealing section 164 includes peelable sealing structure 150. In thevariation depicted in FIG. 3A, peelable sealing structure 150 includessealing layer 152 disposed on additional layer 154. As set forth abovein connection with the descriptions of FIGS. 2A, 2B, and 2C, sealinglayer 152 comprises a thermoplastic polymer and an additive such as anorganoclay dispersed within the thermoplastic polymer.

Still referring to FIGS. 3A and 3B, packaging system 160 furtherincludes a second sealing structure 150′ contacting peelable sealingstructure 150 to form peelable seal 170. Seal 170 seals an opening attop side 172 of packaging system 160. Similar peelable seals areoptionally positioned at bottom side 174, left side 176, and right side178. Peelable sealing structure 150′ also includes sealing layer 152disposed on additional layer 154. Specifically, a first portion of thecombination of sealing layer 152 disposed on additional layer 154 formssealing structure 150 while a second portion of the combination ofsealing layer 152 disposed on additional layer 154 forms sealingstructure 150′. Sealing structures 150, 150′ are continuous withcontainer section 162. In a variation of the present embodiment, a thirdportion of the combination of sealing layer 152 disposed on additionallayer 154 at least partially forms container section 162.Advantageously, packaging system 160 is adapted to contain object(s) 180(i.e., may be one or more objects). Examples of object(s) 180 that maybe packaged include, but are not limited to, food products andsterilized objects (e.g., medical devices).

With reference to FIGS. 4A and 4B, variations of peelable sealingsection 164 as used in a pouch-like packaging systems are illustrated.FIG. 4A is a schematic cross-section of a refinement in which sealinglayer 152 is substantially confined to the vicinity of peelable sealingsection 164. This variation is achieved by either confining theincorporation of organoclay or by depositing a distinct layer in thevicinity of sealing structure 164. This variation further includes innerlayer 182 and one or more additional layer 154. FIG. 4B is a schematiccross-section of a refinement in which packaging system 160 includessecond sealing layer 186 with peelable seal 170 being formed betweenfirst sealing layer 152 and second sealing layer 186. In this latterrefinement, sealing layer 152 extends minimally, if at all, intocontainer section 162. Moreover, in this refinement, container section162 optionally includes liner layer 182 which is different than firstsealing layer 152. In a further refinement of this variation, sealingsection 164 further includes one or more additional polymer layer(s) 154disposed over first sealing layer 152 and/or second sealing layer 186.In a particularly useful example of this refinement, one or moreadditional polymer layer(s) 154 at least partially form containersection 162.

With reference to FIGS. 5A and 5B, variations of packaging systems usingthe peelable sealing structures of the invention with rigid containersections are illustrated. FIG. 5A provides a schematic cross-section ofa cup-like packaging system that uses the peelable seeling structures ofthe invention. Packaging system 190 includes peelable sealing structure150 and sealing opening 192 of container section 194. A peripheralportion of peelable sealing structure 150 is disposed over and contactssubstrate section 196 of container section 194. FIG. 5B provides aschematic cross-section of a blister packaging system that incorporatesmultiple cup-like containers. Blister packaging system 200 includespeelable sealing structure 152 and sealing openings 202, 204 ofcontainer sections 206, 208. A portion of peelable sealing structure 152is disposed over and contacts substrate sections 210, 212 of containersections 206, 208.

As set forth above, the peelable sealing structures of the variousembodiments of the invention include an additive such as organoclays.Examples of useful organoclays include, but are not limited to,kaolinite, montmorillonite-smectite clays, bentonite clays, illiteclays, and combinations thereof. U.S. Pat. Nos. 5,780,376, 5,739,087,6,034,163, and 5,747,560 provide specific examples of nanoclays that areuseful in practicing the present invention. The entire disclosure ofeach of these patents is hereby incorporated by reference. In onerefinement of the present invention, the organoclay is present in anamount from 1 wt % to 20 wt % of the combined weight of thethermoplastic polymer and the organoclay. In another refinement of thepresent embodiment, the organoclay is present in an amount from 2 wt %to 10 wt % of the combined weight of the thermoplastic polymer and theorganoclay.

The organoclay used in peelable sealing layer 152 typically comprises aplurality of particles. In one variation, the organoclay comprises aplurality of particles having at least one spatial dimension less than200 nm. In another variation, the organoclay comprises a plurality ofparticles having at least one spatial dimension less than 100 nm. Inanother variation, the organoclay comprises a plurality of particleshaving at least one spatial dimension less than 50 nm. In still anothervariation, the organoclay comprises a plurality of particles havingspatial dimensions greater than or equal to 1 nm. In still anothervariation, the organoclay comprises a plurality of particles havingspatial dimensions greater than or equal to 5 nm. In another variation,the organoclay comprises platelets having an average separation of atleast 20 angstroms. In yet another variation, the organoclay comprisesplatelets having an average separation of at least 30 angstroms. Instill another variation, the organoclay comprises platelets having anaverage separation of at least 40 angstroms. Typically, before combiningwith the thermoplastic polymer, the organoclay comprises plateletshaving an average separation between 20 and 45 angstroms.Advantageously, upon combining with the thermoplastic, the organoclayremains in this exfoliated state such that the average separation ismaintained or increased.

As set forth above, peelable sealing layer 152 also includes athermoplastic polymer. Suitable thermoplastic polymers include, but arenot limited to, nylons, polyolefins, polystyrenes, polyesters,polycarbonates, and mixtures thereof. In a variation, the thermoplasticpolymer comprises a component selected from the group consisting ofethylene acrylic acid, ethylene ethyl acrylate, ethylene ionomers (e.g.,the Surlyn® line of resins available from E.I. du Pont de Nemours andCompany), and combinations thereof. Polyolefins are particularly usefulthermoplastic polymers in the practice of the invention. In onevariation, the polyolefin is selected from the group consisting ofhomopolymers and copolymers of ethylene, propylene, vinyl acetate, andcombinations thereof. A blend of polyolefins with ethylene vinyl acetate(“EVA”) is found to be particularly useful in forming peelable sealsespecially when the additive is an organoclay.

The container sections of the various embodiments of the invention areformed from virtually any material used for packaging. Such materialsinclude, but are not limited to, paper, metal foil, polymeric sheets,metalized polymeric sheets, and combinations thereof. More specificexamples include, oriented or non-oriented polyester, oriented ornon-oriented polypropylene, oriented or non-oriented nylon, andcombinations thereof. Each of these materials may be coated or uncoated.Examples of useful coatings include, but are not limited to, varnishes,lacquers, adhesives, inks, and barrier materials (i.e., PVDC). Usefulmaterials for packaging medical devices include high densitypolyolefins. Tyvek® (a synthetic material made of high-densitypolyethylene fibers) commercially available from Dupont, Inc. is anexample of a such a material used for packaging medical devices.

In yet another embodiment of the present invention, a method of formingthe packaging systems set forth above is provided. With reference toFIG. 6, a diagram illustrating the method of this embodiment isprovided. A thermoplastic polymer (“TP”) is combined with an organoclay(“OC”) to form an organoclay-polymer blend (“OCB”) in step a). In onevariation, this combining occurs in extruder 220. Sealing layer 152 isthen formed by extrusion from die 222 in step b) from theorganoclay-polymer blend. In a variation, additional layer are formed byproviding material from additional extruders (such as extruder 230) todie 222. In a refinement of the present embodiment, the thermoplasticpolymer and the organclay are premixed in mixer 224 and then introducedinto extruder 220. Typically, sealing layer 152 will be formed alongwith or onto one or more additional layers 154, 156 (as shown in FIG.2). Opened packaging system 160 is then formed in step c). This processmay include steps in which the sides are sealed to produce the pouchstructures of FIGS. 3-4. In a variation, the formation of openedpackaging system 160 occurs during step b).

In a variation of the present embodiment, a thermoplastic polymer iscombined with an organoclay by mixing a master batch with a neatpolymer. In this variation, the master batch comprising the organoclayand at least a portion of the thermoplastic polymer. In this refinement,the master batch typically includes from 10 to 80 wt % organoclay.

The step of forming sealing layer 152 is accomplished by any methodcapable of producing layers or films from thermoplastic compositions.Examples of such methods include, but are not limited to, extrusion,co-extrusion, blow molding, casting, extrusion blow molding, and filmblowing.

Still referring to FIG. 6, the method of the present embodimentoptionally further comprises placing object(s) 180 within open packagingsystem 160 (step d). Typically, object(s) 180 reside within containersection 162. After object(s) 180 are placed within container section162, sealing layer 152 is contacted with a sealing substrate (i.e.,sealing structure 150′) during step e) to form a seal. Sealing may beaccomplished by any number of sealing methods known in the art.Examples, include, but are not limited to, conduction heat sealing,ultrasonic sealing, and induction sealing.

The following examples illustrate the various embodiments of the presentinvention. Those skilled in the art will recognize many variations thatare within the spirit of the present invention and scope of the claims.

FIG. 7A provides plots of the peel force versus temperature for a sealformed from a sealing layer made from a co-extruded HDPE and a LLDPE/EVAand organoclay blend (i.e, a bi-layer). In these experiments, the sealof a sealed bag is pulled apart. Plots for organoclay loadings of 5 and6 wt % are provided. FIG. 7A demonstrates that the seals of theinvention can be opened by a consistent opening force over a sealforming temperature range of 50° F. degrees. Moreover, the seal strengthis observed to be peelable and relatively flat over the temperaturerange 200° F. to 250° F. FIG. 7B provides plots of the peel force versusseal formation temperature. Plots for a reference without organoclay andfor a test sample with 5 wt % organoclay are provided. The referencesample consisted of a 2.4 mil film formed from a three layer coextrusionof high density polyethylene (“HDPE”), ethylene vinyl alcohol, linearlow density polyethylene (“EVOH”), and a blend of ethylene vinyl acetateblend and LLDPE. The test sample consisted of a 2.4 mil film formed froma three layer coextrusion of HDPE, EVOH, and a blend of LLDPE EVA and 5wt % organoclay. The reference and test samples were sealed in aSentinal sealer. Peel force is determined in accordance with ASTM F-88.The seal time for the points in FIG. 7B is 0.50 sec and the seal jawpressure is 30 PSI. It is observed that the variation of the peel forceover the temperature range 175° F. to 265° F. varied less for the samplewith organoclay. Moreover, the seal formed with organoclays is peelableover that entire range of seal formation. FIG. 7C provides a plot of thepeel force versus seal formation temperature for a seal made from a foillaminated to a sealing film. In this experiment, 48 ga PET/50 ga Foil isadhesively laminated to 3.2 mil test film. The test film is made from aLDPE/LLDPE/organoclay blend. The seal is made to a film of the sameconstruction. The reference and test samples are sealed in a Sentinalsealer with peel force being determined in accordance with ASTM F-88.FIG. 7C clearly show a consistent peelable seal being formed attemperatures from 300° F. to 425° F.

Nanoblend™ MB 2001 or Nanoblend™ MB 2101 (“master batches”) is mixedwith a commercial polyethylene (“PE”) blend pouch sealant in asingle-screw extruder with the sealant layer of the invention formed ina second film blowing operation. The tensile properties of the resultingfilms are evaluated in accordance to ASTM D638 (Table 1) with a testspeed of 50 mm/min. Prior to testing, all samples are annealed for 21days at 30° C. Films that include an organoclay are found to have ahigher modulus than films without organoclay without sacrificingstrength or max. elongation. The increase in modulus being 75% for 3 wt% organoclay, 150% for 6 wt % organoclay, and 240% for 9 wt %organoclay.

TABLE 1 Tensile properties of films formed with no added organoclay andvarious amounts of organoclay. Elongation Tensile Tensile at breakModulus (MPa) Strength (MPa) (%) unfilled 306 (±15) 24 (±1) 324 (±11)(0% Clay) unfilled-TS* 329 (±5)  24 (±1) 291 (±5)  (0% Clay) 2001 3%Clay 587 (±9)  23 (±1) 325 (±11) 6% Clay 825 (±17) 24 (±1) 396 (±6)  9%Clay 1129 (±25)  23 (±1) 295 (±23) 2101 3% Clay 581 (±32) 22 (±1) 316(±17) 6% Clay 842 (±33) 25 (±1) 400 (±1)  9% Clay 1106 (±66)  22 (±1)294 (±13) *Unfilled-TS: Twin-screw extruded pure PE

Table 2 summarizes the results of VICAT Heat Deflection Testing. TheVicat Softening Temperature is observed to increase with increasingorganoclay content with a sample having 9 wt % nanoclay exhibiting a 23°C. increase in softening temperature. The data of Table 2 implies thatcrystallinity is substantially uneffected by the addition of organoclayto the polyethylene sealant composition.

TABLE 2 Vicat Softening Temperature as a function of organoclay content.Composition HDT (° C.) unfilled (0% clay) 64.5 3% by Nano2001 70.5 6% byNano2001 80.9 9% by Nano2001 87.0 3% by Nano2101 70.5 6% by Nano210180.5 9% by Nano2101 87.0

Crystallization temperature and melting temperature are also evaluated.These measurements are performed by measuring the enthalpies of fusionand crystallization in accordance with ASTM D 3417. FIG. 8 providesplots for determining the melting temperature (“Tm”) while FIG. 9provides plots for determining the crystallization temperature (“Tc”)for layers containing varying amounts of Nanoblend™ MB 2001. Tm and Tcare observed to be substantially uneffected by the addition of nanoclayas compared to a pure polyethylene sample. FIG. 10A provides a set ofx-ray diffraction plots showing the dispersion of organoclay fromNanoblend 2001 within a sealing layer comprising polyethylene. FIG. 10Bprovides a set of x-ray diffraction plots showing the dispersion oforganoclay from Nanoblend 2101 within a sealing layer comprisingpolyethylene. The x-ray diffraction data demonstrates the meanseparation of organoclay platelets is preserved (i.e., minimalagglomeration). Such preservation of separation allows for the achievedproperties regarding peelability, tensile strength, HDT, and theelongation of break of embodiments of the present invention.

Tables 3 and 4 provide surface roughness measurements for sealing layersformed by the present invention. In these examples, a coextrudedbi-layer is formed. The smoother side is from an HDPE layer not havingorganoclay. The rougher side is a LLDPE/EVA layer having organoclay. Theorganoclay-containing layers of the present invention are found to havea higher degree of roughness than analogous samples not havingorganoclay. Moreover, the sample having 6 wt % organoclay has a greateramount of surface roughness than the sample having 5 wt % organoclaythereby showing that the amount of surface roughness tends to increasein the range of about 10% or less.

TABLE 3 Smoother side of the bi-layer sample having 5 wt % organoclay inthe sealant layer Scan speed (μm/S), vertical range (um) 10, 13 50, 1310, 1048 50, 1048 Average roughness (Ra)/A° 2406 2428 2343 2303 Maximumroughness (Mas 2538 2617 2343 2279 Ra)/A° Roughness (RMS)/A° 2991 30402857 3096

TABLE 4 Rougher side of the bi-layer sample having 5 wt % organoclay inthe sealant layer Scan speed (μm/S), vertical range (um) 10, 13 50, 1310, 1048 50, 1048 Average roughness (R_(A))/A° 6217 5413 5871 5979Maximum roughness 5059 4499 5775 5741 (Max R_(a))/A° Roughness (RMS)/A°7947 6917 7571 7648

TABLE 5 Smoother side of the bi-layer sample having 6 wt % organoclay inthe sealant layer Scan speed (μm/S), vertical range (um) 10, 13 50, 1310, 1048 50, 1048 Average roughness (Ra)(A°) 2564 2275 3110 3210 Maximumroughness 1994 1762 2333 2543 (Max R_(a)) (A°) Roughness (RMS) (A°) 33512999 3843 3445

TABLE 6 Rougher side of the bi-layer sample having 6 wt % organoclay inthe sealant layer Scan speed (μm/S), vertical range (um) 10, 13 50, 1310, 1048 50, 1048 Average roughness (R_(a)) (A°) 7069 6935 7974 6897Maximum roughness 8081 6977 6600 6412 (Max R_(a)) (A°) Roughness(RMS)/A° 9100 8990 9955 8951

FIG. 11 provides plots of seal strength versus seal formationtemperature. In these experiments an impulse sealer is used for formingthe seals. In such sealers the temperature is set by a dial position.FIG. 11 provides the seal strength as a function of dial position.Estimated temperatures are provided at the top of FIG. 11. FIG. 11,again, demonstrates the synergistic effect of the combinationpolyethylene, EVA, and organoclay with seals formed from thiscombination being peelable over a wide seal formation temperature range.

A series of 25.4 mm seals are made at a pressure of about 1000 psi witha sealing time of about 8 seconds. In these experiments a hydraulicpress is used. Although these conditions are harsher than the conditionsused in typical commercial sealing operations, the formations ofpeelable seals at these conditions further illustrates the ability ofthe formulations of the present invention to form peelable seal. FIGS.12A and 12B provides plots of the seal strength versus seal formationtemperature for various combinations of seal layers. In theseexperiments a seal is formed between a first sealing layer and a secondsealing layer. In FIG. 12A each sealing layer includes polyethylene or ablend of polyethylene and EVA. In general, the seal strength increaseswith increasing temperature for these combinations over the temperaturerange 110° C. to 140° C. In FIG. 12B, at least one of the sealing layersincludes a blend of polyethylene, EVA, and organoclay. For seals formedin this manner, FIG. 12B illustrates the formation of peelable sealsover a temperature range from 110° C. to 140° C. FIGS. 13A and 13Bprovide Table 6 which summarizes the seal strength data for FIGS. 12Aand 12B while characterizing the type of failure mode (see FIGS. 1A-1G).Table 6 clearly shows the formation of peelable seals over a wide rangeof temperatures.

In still another embodiment of the present invention, a peelable sealadapted to provide a leak-proof seal having one or more wrinklesincorporated therein is provided. With reference to FIGS. 14A and 14B,schematic cross-sections illustration of peelable seals incorporatingone or more folds are provided. Peelable seal 250 includes first sealinglayer 252 and second sealing layer 254. First sealing layer 252 includebends 258, 260 and fold 262. Similarly, second sealing layer 254includes bends 264, 266. First layer sealing layer 252 includes firstsealing surface 270 while second sealing layer 254 includes secondsealing surface 272. Outer sealing surfaces 274, 276 are attached toadditional layers as set forth above in connection with the descriptionsof FIGS. 1-5. First sealing surface 270 contacts the second sealingsurface 272 to form seal 280. FIG. 14B provides an illustration in whichsecond sealing layer 254 includes minimal bends or folds.

The details of the composition of sealing layers 252 and 254 are thesame as those set forth above. In particular, at least one of the firstsealing layer 252 and second sealing layer 254 include a thermoplasticpolymer and an additive dispersed within the thermoplastic polymer. In avariation, the additive is present in a sufficient amount to formpeelable seal 280 between the first sealing layer 252 and second sealinglayer 254 at all temperatures within a peelable seal temperature range.As set forth above, in a refinement, the peelable seal temperature rangeis from a seal initiation temperature to a temperature that is at least100 F degrees above the seal initiation temperature. In a particularlyuseful variation, the additive is an organoclay dispersed within atleast a portion of the thermoplastic polymer. In such a variation, oneor both of first sealing layer 252 and second sealing layer 254 have aseal initiation temperature from about 170° F. to about 350° F.Additional details for the additive, the organoclay and thethermoplastic polymer are set forth above.

With reference to FIG. 15, a top view of a packaging system that tendsto have folds or bends incorporated within the seals is provided.Package 290 includes peelable seals 292, 294, 296. It should beappreciated that packaging with only one or two side having a peelableseal are also possible. Package 290 is depicted as containing food item298. The presence of food item 298 within container section 300 duringthe packaging process causes a lifting of container wall 302. Thislifting of container wall 302 induces the formation of bends and foldwithin peelable seals 292, 294, 296 as set forth in connection with thedescriptions of FIGS. 14A and 14B. Packages such as those depicted inFIG. 15 are found to have a reduced incidence of leaks. For example,oxygen levels in a package using the organoclay compositions set forthabove are found to be on average lower than a commercially availablesealing composition. Moreover, test with liquids containing dyes arealso found to have low incidence of leaks.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

What is claimed is:
 1. A method of forming a packaging system thatincludes a sealing layer, the method comprising: combining athermoplastic polymer with an organoclay to form an organoclay-polymerblend, the organoclay comprising platelets having an average separationof at least 20 angstroms; forming the sealing layer from theorganoclay-polymer blend, the sealing layer having a seal initiationtemperature from about 170° F. to about 350° F. and a tensile modulusfrom about 500 to about 2000 MPa; and forming an open packaging systemfrom the sealing layer.
 2. The method of claim 1 wherein the step offorming the sealing layer is accomplished by extrusion, co-extrusion,blow molding, casting, extrusion blow molding, and film blowing.
 3. Themethod of claim 1 wherein the sealing layer is formed by extrusion froma die.
 4. The method of claim 1 wherein the thermoplastic polymer andthe organoclay organoclay are premixed and then introduced into anextruder.
 5. The method of claim 1 further comprising forming additionallayers by providing material from additional extruders.
 6. The method ofclaim 1 further comprising sealing the open packaging system.
 7. Themethod of claim 6 wherein an object is placed in the open packagingsystem prior to sealing.
 8. The method of claim 6 wherein the sealinglayer is formed by contacting the layer with a sealing substrate.
 9. Themethod of claim 8 wherein the sealing layer is formed by conduction heatsealing, ultrasonic sealing, or induction sealing.
 10. The method ofclaim 1 wherein the thermoplastic polymer is combined with theorganoclay by mixing a master batch with a neat polymer.
 11. The methodof claim 10 wherein the master batch includes from 10 to 80 wt %organoclay.
 12. The method of claim 1 wherein the sealing layer isformable into a peelable seal at all temperatures within a peelable sealtemperature range, the peelable seal temperature range being from theseal initiation temperature to a temperature that is at least 100° F.above the seal initiation temperature.
 13. The method of claim 1 whereinthe organoclay comprises a plurality of particles having a spatialdimension less than 200 nm.
 14. The method of claim 1 wherein theaverage separation is between 20 to 45 angstroms.
 15. The method ofclaim 1 wherein the platelets have an average separation of at least 30angstroms.
 16. The method of claim 1 wherein the organoclay comprises aclay selected from the group consisting of kaolinite,montmorillonite-smectite clays, bentonite clays, illite clays, andcombinations thereof.
 17. The method of claim 1 wherein the organoclayis present in an amount from 1 wt % to 20 wt % of the combined weight ofthe thermoplastic polymer and the organoclay.
 18. The method of claim 1wherein the organoclay is present in an amount from 2 wt % to 10 wt % ofthe combined weight of the thermoplastic polymer and the organoclay. 19.The method of claim 1 wherein the thermoplastic polymer furthercomprises a component selected from the group consisting of nylons,polyolefins, polystyrenes, polyesters, polycarbonates, copolymers ofethylene, copolymers of propylene, ethylene vinyl acetate, and mixturesthereof.
 20. The method of claim 1 wherein the thermoplastic polymercomprises a component selected from the group consisting of ethyleneacrylic acid, ethylene ethyl acrylate, ethylene ionomers, andcombinations thereof.